The present invention relates to an apparatus for processing lumpy and advantageously spherical material, such as pellets, so that the lumpy material can be applied on an essentially continuously moving surface to form a layer which is advantageous both in thickness and in cross-section, so that in the further processing of the lumpy material, the gas to be conducted through said layer can be made to penetrate the layer in an essentially homogeneous fashion.
Several smelting processes require that the material to be fed into smelting is not too finely divided. Therefore a finely ground material such as concentrate must first be pelletized and thereafter sintered in order to improve the strength of the pellets. The sintering can be carried out for instance in a conveyor-type furnace where hot gas is blown in the pellet bed in order to sinter the wet pellets. For obtaining a homogeneous sintering product, the hot gas must be allowed to flow through the pellet bed in an essentially even fashion. For creating an even gas flow, also the pellet bed must be essentially even in thickness, so that the whole pellet bed is treated in a way that is advantageous for the sintering product.
In the processing of lumpy, essentially spherical material, it is important to take into account the special feature of the material, i.e. its round surface, which makes the material move piece by piece. When this type of lumpy material should be applied as an essentially even layer, it easily happens that without special procedures the layer becomes very thick in the middle and becomes thinner towards the edges. In thickness, such a layer does not satisfy the requirements of an essentially even layer.
Lumpy and essentially spherical material can be processed, in order to obtain a layer that is essentially even in thickness, for example by conveying the material on a conveyor which is articulated at one end, so that the free end of the conveyor moves along a spherical orbit, according to the width of a second conveyor located underneath the first conveyor. This kind of combination requires a lot of space in the lengthwise direction, because the conveyors are arranged in succession. In order to obtain an even layer, the material can also be conveyed by moving back and forth a chain-operated conveyor provided with a crank lever mechanism, so that the material is fed in this conveyor at one end, and it drops further onto a transversal conveyor located underneath this first conveyor. The drawback of a chain-operated conveyor is that the thickness of the material layer created on the lower conveyor can only be adjusted by changing the chain wheels. This in turn requires that the chain lengths are altered, and further that the conveyor transfer rate and stroke are adjusted.
The object of the present invention is to eliminate some of the drawbacks of the prior art and to achieve an improved apparatus for processing lumpy and essentially spherical material, wherein the lumpy material is applied on an essentially continuously moving surface in a layer that is advantageous both in thickness and in cross-section, so that the gases to be conducted through said layer in the further processing of the lumpy material are made to penetrate the layer in an essentially even fashion. The essential novel features of the invention are apparent from the appended claims.
According to the invention, the apparatus for processing lumpy material is provided with an essentially continuously operated belt conveyor, which moves back and forth between two positions in relation to a second conveyor located underneath the first conveyor. The opposite positions of the alternating motion are chosen so that the material discharged from the belt conveyor drops onto the conveyor surface of the second conveyor placed underneath the belt conveyor essentially along the whole width of the conveyor surface. The alternating motion of the belt conveyor is created by a specific moving member connected to the conveyor, advantageously a hydraulic cylinder provided with a double piston. Other corresponding members that are operated for instance electrically can likewise be employed as the moving members.
According to the invention, the speed of the moving member of the belt conveyor can be steplessly adjusted. Moreover, on the trajectory of the moving member, advantageously near to both ends of the trajectory, there are provided, movably in the lengthwise direction of the trajectory, at least two limit switches whereby the speed of the alternating motion of the belt conveyor can be adjusted near the end of the trajectory of the belt conveyor. When approaching the end of the trajectory, the motion of the belt conveyor is advantageously slowed down by means of the limit switch located first in the proceeding direction. Now the second limit switch in the proceeding direction is placed at the end of the trajectory, and by means of said second limit switch the motion of the belt conveyor is respectively made to speed up, when the belt conveyor starts moving from the end of the trajectory back towards the first limit switch. By means of the location of the first limit switch of the trajectory, it is also possible to adjust the required delay times of the motion of the belt conveyor at both ends of the trajectory. Moreover, by adjusting the speed of motion of the belt conveyor, the quantity of material fed on the second conveyor located underneath the belt conveyor can also be adjusted in the transversal direction of the conveyor belt.
In the apparatus according to the invention, the belt of the belt conveyor is made to rotate so that the belt speed in relation to the quantity of the lumpy material fed thereon is essentially constant irrespective of the position and motional direction of the belt conveyor. The motion of the belt in the belt conveyor is achieved by means of an electric motor or a hydraulic motor. The belt speed of the belt conveyor is advantageously adjusted according to the motional speed, so that the belt conveyor feeds lumpy material onto the second conveyor placed below only when the belt conveyor is returning from that position on the belt conveyor trajectory that is located farthest with respect to the moving member of the belt conveyor. When the belt conveyor is moving from the position on the belt conveyor trajectory that is located nearest with respect to the moving member of the belt conveyor towards the position that is located farthest therefrom, the belt speed of the belt conveyor is advantageously the same as the motional speed of the belt conveyor, in which case the belt speed of the belt conveyor with respect to the belt conveyor proper is zero. When the belt conveyor now moves back from the position on the trajectory that is located farthest in relation to the moving member of the belt conveyor, the speed of the belt conveyor belt is doubled. As a result, on the belt conveyor there always is provided an essentially even layer of lumpy material, which essentially helps in the further processing of the lumpy material.